1. Field of the Invention
The invention relates in general to a three-dimensional dual-band antenna, and more particularly to a three-dimensional dual-band antenna having broadband characteristic.
2. Description of the Related Art
Antennas are important in communication industry which has gained rapid advance in recent years. In general, antennas are used in various small-sized electronic devices such as notebook computers or portable electronic devices.
Antennas can be categorized into planar antennas and three-dimensional antennas; and both types of antennas are capable of receiving/transmitting radiation electromagnetic field. In general, the three-dimensional antenna has better performance. The three-dimensional antenna is exemplified below in receiving the radiation electromagnetic field; and the reasons for the superior performance of the three-dimensional antenna are also disclosed.
Antennas are normally disposed on a circuit board having circuit elements. The radiation electromagnetic field received by the antenna located at the receiver is transmitted by the standing antenna of the base station. In comparison to the planar antenna, the three-dimensional antenna is less affected by the shielding effect of the circuit element.
Moreover, the current flows in the three-dimensional antenna are distributed in both the horizontal direction and the vertical direction. The horizontal direction is the direction parallel with the circuit board; and the vertical direction is the direction parallel with the standing antenna of the base station. In comparison to the planar antenna whose current flow is distributed only in the horizontal direction, the three-dimensional antenna has higher radiation electromagnetic field stability between the standing antenna of the base station.
When the planar antenna receives the radiation electromagnetic field, the current flow is distributed in the horizontal direction and transmitted to the circuit elements disposed on the circuit board. Since the current flows of the circuit elements are normally in the horizontal direction, the current of the planar antenna generates electromagnetic interference which affects the circuit element. However, when the three-dimensional antenna receives the radiation electromagnetic field, the current is distributed in the horizontal direction as well as the current path in the vertical direction. Thus, the current distributed in the horizontal direction is not so high, and the electromagnetic interference effect is reduced accordingly.
However, the conventional three-dimensional antenna normally has a huge volume, and the volume of the three-dimensional dual-band antenna is even larger. Moreover, the communication bandwidth at which the conventional three-dimensional antenna is operated is restricted. Thus, how to provide a small-sized three-dimensional dual-band antenna having broadband is a prominent for the industries.